For purposes of preparing a well for the production of oil or gas, various fluid barriers may be created downhole. For example, in a fracturing operation, a fluid barrier may be formed in the well inside a tubing string for purposes of diverting fracturing fluid into the surrounding formation. As other examples, a fluid barrier may be formed in the well for purposes of pressurizing a tubing string to fire a tubing conveyed pressure (TCP) perforating gun or for purposes of developing a pressure to shift open a string-conveyed valve assembly.